Switching direct-current (DC) to DC voltage converters are used in a variety of applications for converting power at an input voltage into power at a desired output voltage. Such voltage converters are used to power loads such as battery chargers, microprocessors, servers, computers, televisions, and many other electronic devices. Voltage converters may step an input voltage up or down but, for brevity and clarity of explanation, the following background description focuses on step-down converters.
Buck converters represent a common type of non-isolated step-down converter wherein an electronic switch converts an input DC voltage into an alternating-current (AC) voltage that is applied to an inductor. The switch and the inductor, together with some type of rectifier, serve to step down the input voltage and step up the input current, such that a lower voltage and a higher current is provided at the output of the converter. The output voltage (or current) may be regulated by adjusting a frequency and/or duty cycle with which the electronic switch is switched, so as to maintain a relatively constant voltage (or current) at the output. However, such converters suffer relatively high power losses in both the switching and in the inductor. In particular, the entirety of the output current must pass through the inductor. While the resistive losses of an inductor are preferably minimized, they cannot be eliminated and can lead to significant power losses for high output currents. Furthermore, the voltage drop across the inductor is proportional to its inductance, and a large inductance must be used to support buck converters with large step-down ratios. Hence, large, bulky, and expensive inductors are required to support high input-to-output voltage ratios, and high output currents flowing through such inductors. For these reasons, buck converters are typically avoided for applications that require large step-down ratios.
Switched-capacitor converters (SCCs), including converters based upon Dickson or similar charge pumps, use a series of electronic switches and capacitors to step down an input voltage. SCCs are typically more efficient than inductor-based buck converters for relatively high voltage step-down ratios, and do not require large magnetic components (e.g., inductors). However, conventional SCCs are only capable of providing discrete/fixed step-down ratios, e.g., 2:1, 3:2, 6:1, and are not amenable to regulation. Hence, conventional SCCs are not appropriate, at least on their own, for supplying power to loads that require a relatively constant voltage.
Converter circuit topologies and associated techniques are desired that are capable of regulating an output voltage while achieving high efficiency, having low converter impedance, and avoiding large magnetic or other components.